I notice a lot of folks compare the DT531 with the likes of the DT770 and DT880 for comfort, but as already touched upon by Iron Dreamer, the DT770 & 880 certainly are not as comfortable as the DT531. For a start the DT770 Pro has quite a small headband, so it could be a tight fit... of course you can take the leather pad off the headband for a bit more room, but I certainly didnt like the feel of it. Either on or off, I felt the headband burned my scalp, and the clamping force and weight was noticably more than the DT531 which has no scalp burn, clamping force is just right, and the pads are soft and non itchy.
The only other headphone that I've tried that comes close is the CD3000.
Other headphones have other flaws that dont make them that great IMO:-
Grado - need I say more?
Senn 6xx - Highish clamping force, itchy pads
Sony CD1700 - Itchy pads
Beyer 770/880/990 - Headband too small, scalp burn
Beyer 831/931 - Close, but the weight still make it slightly worse than DT 531.
AKG K2xx - Dont like the pad material, sticky and sweaty, clamping force
All IMHO of course.